Determination methods for steady-state concentrations of HO• and SO4•− in electrochemical advanced oxidation processes

• Published in: Chemosphere (Oxford) Vol. 261; p. 127658
• Main Authors: Yang, Sui-Qin, Cui, Yu-Hong, Li, Jia-Ying, Lv, Xu-Dong, Liu, Zheng-Qian
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2020
• Subjects: Competitive kinetics; Electrochemical advanced oxidation processes; Hydroxyl radical; Radical steady-state concentration; Scavenging assay; Sulfate radical; Sulfate radical; Electrochemical advanced oxidation processes; Scavenging assay; Competitive kinetics; Hydroxyl radical; Radical steady-state concentration
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2020.127658

Competitive kinetics and scavenging assay are commonly used for radical quantification. However, the accuracy of the two methods has been challenged in electrochemical advanced oxidation processes (EAOPs) since the strong reactivity of electrode against organic indicators may disrupt the quantitative relationship between indicator consumption and radical concentration. The present study focused on screening suitable indicators and developing suitable methods for determining the steady-state concentrations of SO4•− and HO• ([SO4•−]ss and [HO•]ss) in several EAOPs for water treatment based on competitive kinetics and scavenging assay. The applicability of the modified methods and available indicators were investigated through experimental and kinetic analysis. In anode alone process, the competitive kinetics was more appropriate than scavenging assay and benzoic acid (BA) met the basic requirement of being a competitor to determine the [HO•]ss. In cathode alone process, BA was more resistant to interfering factors than other competitors (ibuprofen, atrazine and nitrobenzene) and its reaction rate involved only the radical oxidation even when the reaction conditions varied over a wide range. Therefore, the [HO•]ss could be obtained by the competitive kinetic equation of BA when HO• existed alone. When HO• coexisted with SO4•−, a two-step method combining scavenging assay and competitive kinetics was proposed to measure [SO4•−]ss and [HO•]ss, in which tert-butyl alcohol and BA were added as scavenger and competitor, respectively. Furthermore, the reliability of each approach was verified by the experimental results and kinetic analysis. [Display omitted] •Steady-state concentrations of HO• and SO4•−([HO•]ss and [SO4•−]ss) in EAOPs are determined.•BA can be used as a competitor in EAOPs.•A two-step method combining competitive kinetics and scavenging assay is proposed.•The coexisted [HO•]ss and [SO4•−]ss can be obtained by the two-step method.•The experimental results of each method agree well with the theoretical prediction.